Non-eruption of a developing mandibular first permanent molar

Published: November 2014

Bulletin
#38 – November 2014

Non-eruption of a developing mandibular
first permanent molar

Examination

The patient was an 8.3 year old boy, tall for his age, with
a convex profile due to a mildly procumbent maxilla. Intra-orally he presented
with a class 2 division 1 type of occlusion, with an enlarged overjet and much
anterior dental spacing in both jaws. The erupted permanent dentition was
remarkable for the relatively large size of the individual teeth, but it
included only 2 maxillary central incisors, 3 mandibular incisors and 3 of the
first permanent molars. The remaining teeth were deciduous.

Fig. 1. Panoramic view from March 2011 at age 7.1 years.
Note congenital absence of a single permanent mandibular incisor and
bilaterally of second premolars and second permanent molars. The right
mandibular first molar is impacted and held down in the body of the mandible.
Its follicle appeared marginally enlarged.

He was first brought to see me in May of 2012, armed with a
panoramic film that had been taken in March of 2011, when he was 7.1 years old. The film showed the apparent congenital
absence in the mandible of the left central incisor, both second premolars and
both second molars of the permanent series (Fig. 1). The maxillary dentition was complete and, at
that age, it was premature to relate to the absence of signs of calcification
of third molars. The film showed erupted first permanent molars and a full
complement of deciduous teeth in the maxilla. In the mandible, a single
permanent incisor and the left first permanent molar were present, together
with deciduous canines and molars and a single deciduous incisor.

The mandibular right first molar was absent from the erupted
dentition, but could be seen on the radiograph. It was upright but located very
low down in the basal bone, with short developing roots, close to the lower
border of the mandible. Its crown was encompassed by an enlarged follicle and
covered by bone superiorly. The roots of this molar were less than half the
length of the roots of the erupted first molar of the opposite side, although
the degree of apexification appeared similar in each.

Fig. 2. Panoramic view from May 2012 at age 8.3 years.
There has been little notable progress in the position of the impacted molar.
Note the distally hooked root apices close to the lower border of the mandible.

In a second panoramic view which had been commissioned at
the time of this first examination in May 2012 (Fig. 2), the 3 existing
mandibular permanent incisors and the maxillary central incisors had erupted,
while the unerupted mandibular right first molar remained at much the same
level as before, with the exception that its roots had each developed a
distal-facing hooked end, within the compact bone that forms the inferior
mandibular border. From these films, the exact location of this impacted molar
was clear to see and required no further elucidation. For this specific task,
therefore, additional sophisticated radiography or computerized tomography
would be superfluous.

Diagnosis

Teeth normally erupt. In the absence of eruption, it must be
assumed that there is some pathologic cause. The key to success in resolving the
present and any similar tooth impaction, therefore, is to find the cause and,
if possible, eliminate it.Accordingly,
the existing radiographs of this patient were analyzed carefully for signs of
pathology which, in the event, revealed no clue as to the reason for the failure
of the tooth to erupt, other than the fact of the enlarged follicle.

Could this follicle be the reason for the non-eruption? It
is known that unerupted teeth often develop enlarged follicles, but is this the
outcome of the non-eruption or is it its cause?

We know that a typical dentigerous cyst, which is etiologically,
anatomically and histologically the logical extension of an enlarged follicle
(only semantics and timing differentiate between the two), will drive the
encompassed tooth to back-up along its former eruption path, because its
intra-cystic hydrostatic pressure overwhelms the force of eruption. It causes
adjacent teeth to be pushed aside, as it enlarges still further, thinning out
the surrounding bone as it goes. It will, as we see in the case presented here,
push the developing root apices downward against the compact bone of the lower
border of the mandible and will curl these apices in defiance of the hypothesis
of the immutability of location of the developing root apex.1

Fig 3a. A 3D screenshot from the CBCT.

Fig. 3b. CBCT panoramic views. In the upper picture, the
red line represents a tracing of the inferior alveolar nerve canal. The lower
picture shows the location of the transaxial 1mm slices.

Fig. 3c. CBCT transaxial slice #39 showing the inferior
dental canal (arrow) on the lingual side of the root of the molar.

Aside from this
potential etiologic factor, the single remaining macroscopic etiologic factor
for non-eruption that needed to be checked, was the possible involvement of its
developing roots with the infra-alveolar nerve bundle. This can only be
successfully done using cone beam CT2, 3 and, given the seriousness
of the implications of this possible diagnosis, a CBCT examination was
considered entirely justified. As can be seen in figure 3a-c, no such
involvement was found. The cause for the impaction was therefore assumed to be
its enlarged follicle.

Treatment options

Given this exhaustive elimination of all known etiologic
factors, the parents were offered two lines of possible treatment, namely either
to attempt to raise the tooth using routine orthodontic traction or to extract
it.

In the absence of a definitive watertight etiology, the
prognosis for raising the tooth was uncertain and the justification for the
treatment largely empirical. On the other hand, extracting a molar tooth in a
dentition already exhibiting 5 missing teeth in the same jaw, rendered this alternative
even less palatable. The parents were informed and accepted that the first line
of treatment should be undertaken, understanding that the chances of success
could not be gauged. Nevertheless, they were made aware that, in the event of
failure, the second line of treatment still remained a viable option.

Treatment for the overall class 2 malocclusion and
generalized spacing was not considered justified at this early age, since
further treatment would be needed in the permanent dentition and the longevity
of the deciduous teeth which were without successors, could not be estimated so
early. The treatment therefore was
confined to the resolution of the impacted molar, as a phase 1 procedure only.

The sole orthodontic force system needed in this case was
the application of vertical traction to the tooth. For this to be effective, a
solid anchor base needed to be provided and the following options were considered:-

1.

1.A fixed orthodontic
appliance based on all the mandibular teeth, with a distal, free-ended extension
of the archwire to be used as a spring when activated vertically.

There
is a significant drawback with this method because of a relative inability to
establish a significant height differential between the mucosa covering the
alveolar crest and the occlusal plane, in the molar area. The reactive force to
vertical traction in this case would apply an intrusive component on the
immediately adjacent deciduous second molar whose roots are unresorbed and
beneath which there is no permanent successor. This tooth is a very valuable
unit for the patient and its preservation is highly desirable. It was
considered that intrusive orthodontic forces applied to it could elicit
resorption of its roots, reducing its long term prognosis.

2.A maxillary fixed appliance
using an intermaxillary elastic, to be changed by the patient on a day-to-day
basis.

In
similar fashion, vertical traction would cause over-eruption of the teeth of
that side, generating a cant in the occlusal plane. Specifically, however, the
maxillary first molar was unopposed due to the absence (impaction) of its
antagonist and any change in its vertical status (over-eruption) would reduce
the degree to which the impacted tooth could be erupted.

3.A temporary anchorage
device placed in the maxilla, against which the patient would apply an
intermaxillary elastic, to be changed on a day-to-day basis. Since this
approach did not use dental anchorage, harmful effect on adjacent or opposing
teeth would be avoided.

A critical comparison of these 3 treatment modalities
revealed that the third option was judged the simplest, the most efficient and cost-effective method.

Surgery

In early January 2013, the patient was admitted as a “day-care
hospitalization” surgical case, in which the mandibular molar was exposed and
two attachments bonded to it. At the same time, a zygomatic plate was placed in
the opposing jaw. This double procedure was performed in the hospital operating
theatre,under general anesthetic with appropriate intubation.

Fig. 4a. Intra-oral view showing the exposed molar with
two attachments in place with twisted stainless steel ligatures.

Fig. 4b. Intra-oral view of the sutured exposure site
with two hooked ligatures.

In the mandible, a buccal and a lingual flap were reflected
and bone cleared from the occlusal and buccal surfaces of the crown of the
impacted molar. The dental follicle was removed only in the exposed area and no
attempt was made to open it on the lingual, mesial or distal surfaces of the
tooth, nor was this clearance extended to the CEJ in the exposed areas.Given the fairly large area of buccal surface
now visible, two simple eyelet attachments were bonded by the orthodontist,4while the surgeon
maintained meticulous hemostasis, as is demanded with the acid etch bonding
technique (Fig. 4a).

It is important to point out and to emphasize that surgical
exposure of an impacted tooth should be a 4-handed procedure involving both
orthodontist and oral surgeon, which is critical for the success of the entire
treatment. Optimal conditions must be achieved to ensure a securely bonded
attachment. Neither the orthodontist nor the surgeon and certainly not the
patient are interested in failure and the need for a repeat performance!

In many cases, an oral and maxillofacial surgeon (OMFS) working
only with chairside assistance will fail to achieve a good exposure with a
reliably bonded attachment, for one or more of many reasons.5 The
OMFS is not as skilful, adroit, or precise as the orthodontist at bonding
attachments, since it is not a procedure that he/she executes more than once or
twice a month, while the orthodontist performs it on hundreds of teeth each
week. The orthodontist knows exactly where the attachment needs to be placed,
with what connector and in which direction to draw it through to the exterior.
Furthermore, even the most practiced chairside assistant cannot hold back
surgical flaps nor control bleeding points with the same degree of expertise as
the OMFS, who is often able to manipulate freshly cut and bleeding tissues in almost
inaccessible locations, to permit successful bonding. If this cri-de-coeur is
heard and the present protocol for the exposure procedure is universally adopted,
fewer impacted teeth will be sacrificed and the failure rate of those that are
attempted will plummet.

The eyelets were pre-ligated with a fairly heavy (0.014”)
soft ligature wire, which was twisted into a braid prior to the procedure. The
surgical flaps were replaced completely in the manner of a closed surgical
exposure procedure. The excess length of the twisted ligatures was cut off and
the shortened ends turned into two small hooks (Fig. 4b).

Fig. 5a. Intra-oral view of the inferior surface of the
zygomatic process of the maxilla. The L-shaped plate is secured by 3 screws and
the long arm can be seen to emerge from the attached gingiva adjacent to the
molar.

Fig. 5b. With the surgical incision sutured and the cheek
retracted, only the hooked extremity of the plate can be seen in the sulcus
(arrow).

In the maxilla, a broad longitudinal incision was made high
in the oral mucosa of the sulcus and the inferior border of the zygomatic
process of the maxilla was exposed.6, 7 An L-shaped plate was
fashioned to conform with the contour of the bone surface and its shorter arm
secured into place with 3 titanium screws. Its longer arm was drawn inferiorly
under the oral mucosa and made to exit to the buccal sulcus through the
attached gingiva adjacent to the first permanent molar (Fig. 5a, b). Its
exposed extremity was shaped into a hook prior to its being secured to the zygomatic
plate. After checking for good stability, the initial incision flaps were drawn
back to their former places and re-sutured.

Fig. 6. The immediate post-surgical panoramic view shows
the two bonded eyelets and their twisted ligatures and the L-shaped TAD in
place (January 2013)

A week later, sutures were removed by the surgeon and the
patient referred back to me for the application of extrusive traction, with a
new panoramic radiograph (Fig. 6).

Orthodontics

Back in the orthodontic office 3 weeks later, the child was seen
together with a parent and was found to be healing most satisfactorily. The
repairing surgical flaps were no longer painful, although there was a degree of
sensitivity to manipulation in the area.The patient and parent were taught how to place a small (1/4” medium) latex
elastic between the most accessible of the two twisted ligature hooks that
emanated from the unerupted mandibular molar and the exposed turned up end of
the zygomatic plate.

In contrast to experience with many other patients in
similar circumstances, this particular child found placement of the rubber band
difficult and was only discharged when the parent could prove an ability to
place it with ease. The boy appeared to show evidence of reduced manual
dexterity and, over the subsequent months, the rubber bands were placed by a
parent. However, the parents were less than 100% reliable and many days were lost
each month with no rubber band in place.

Fig. 7. A progress panoramic film showing improvement in
the position of the impacted molar (June 2013).

In the space of 16 months from the initiation of extrusive
traction, the molar slowly improved its position (Fig. 7) to eventually erupt
in its place in the arch. In the June 2014 panoramic radiograph, the root
apices of both mandibular molars had closed, but the treated molar exhibited a
mere half the root length of its unaffected antimere.Interestingly, with the child now 10.2 years
old, early calcification of 3 new molar teeth was evident on the film (Fig. 8).
At this point the patient was referred back to the surgeon for removal of the
zygomatic plate.

Fig. 8. At the completion of treatment, the molar has
been fully erupted and has short roots, compared with its antimere. The patient
was referred back to the oral surgeon at this time, for removal of the L-shaped
plate (July 2014). Note the early development of 3 molars.

Postscript

A word regarding attachments and connectors is in order
here. The purpose of bonding an attachment is for the orthodontist to be able
to apply a traction force and to generally control the movement of an impacted
tooth which is otherwise inaccessible. Most orthodontists use regular brackets
for this purpose, which have many significant disadvantages, as follows:-

1.Standard prescription brackets
are endowed with carefully calculated precision tip and torque values that are
valid only if the bracket is ideally placed on the mid-buccal site of the crown,
with the slot at a predetermined height and oriented in line with the long axis
of the tooth. Access is rarely adequate to achieve these idyllic conditions for
impacted teeth and a compromise location will need to be chosen, reducing the
efficiency of the traction.

2.The contoured base of the
bracket is rarely suited to the surface that is available for bonding, making for
a less reliable bond.4, 5

3.The bracket is very bulky
with a sharp profile, which makes for irritation and inflammation of the
gingiva when the tooth begins to emerge through it and into the oral cavity.

4.An eyelet, welded to a soft
steel tape base, is small and pliable, making it adaptable to any tooth
surface. If it is bonded with the eyelet loop in line with the long axis of the
tooth, a fine nickel-titanium archwire can often be threaded directly through
it, in the latter stages after eruption, to materially assist in alignment.

5.A gold chain is very
popular among orthodontists for use as a connector between the attachment and
the traction spring or elastic chain/thread, but it cannot be used in the
present context. Gravity dictates that it collapses down for a mandibular tooth,
occasionally getting “lost” in in the healing tissues of an open exposure. It offers no means by which an intermaxillary
elastic may be attached to it, by the patient.